(a) Field
The present disclosure relates to an LED emitting device and a driving method thereof.
(b) Description of the Related Art
An AC-DC converter included in an LED emitting device converts an AC input into a DC voltage for emitting an LED. The LED emitting device includes a plurality of LEDs that are connected in series. Hereinafter, the LEDs connected in series will be called an LED string.
The DC voltage output by the AC-DC converter is supplied to the LED string, and in this instance, the DC voltage is controlled with a predetermined voltage that is greater than a forward voltage for the LED string to emit light. In this instance, the predetermined voltage is established to have an optimized level in consideration of power consumption.
While power is supplied to the LED string, an LED may be separated from the LED string, and the LED can be attached to the LED string in an open lamp state. Particularly, when the LED is attached to the LED string, a transient current that is greater than a rated current allowable for the LED string is generated so that the LED of the LED string may be damaged.
In detail, when a degraded LED is replaced with a new LED in the LED string, the degraded LED is separated from the LED string (i.e., to be in the open lamp state), and a new LED is attached to the LED string. In this instance, an output capacitor connected to an output terminal of the AC-DC converter can output a transient current that may damage at least some of the LEDs in the LED string.
Accordingly, the conventional emitting device generates the transient current after it is changed to the normal state from the open lamp state so it may damage the LED.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.